1. Field of the Invention
The present invention generally relates to multilayer polymer-quantum dot light emitting diodes (PQD-LED) and methods of making and using thereof.
2. Description of the Related Art
Polymer-quantum dot light emitting diodes (PQD-LED) have caught immense attention in the LED research and commercial communities by virtue of the marriage of easy processibility and ruggedness of polymers and exotic optical properties of quantum dots (QDs). Many unilayer and bilayer PQD-LEDs have been reported. See Colvin, V. L., et al. (1994) Nature 370:354; Dabbousi, B. O., et al. (1995) Appl. Phys. Lett. 66:1316; Mattousi, H., et al. (1998) J. Appl. Phys. 83:7965–7974; and Schlamp, M. C., et al. (1997) J. Appl. Phys. 82:5837–5842. Unilayer PQD-LEDs have conductive and emissive species mixed together and are far below the theoretical performance limits. Bilayer LEDs perform better than unilayer devices. Unfortunately, bilayer LEDs employ the QD layer as both emissive and electron conducting layer which creates imbalance in charge conduction due to poor conductivity of these colloidal QDs. See Leatherdale, C. A., et al. (2000) Phys. Rev. B. 62:2669–2680. Further in bilayer LEDs the emissive QD layer is next to the metal electrode which causes quenching of emission See Wu, C. C., et al. (1997) IEEE Trans. Electron Devices 44(8):1269; and Becker, H. (1997) Phys. Rev. B 56:1893–1905. Some researchers have also demonstrated PQD-LEDs by electrostatic self assembly, but this process involves a large number of steps and also relies on polycations or polyanions, which are charged and are reported to cause quenching of emission See Chen, W., et al. (2002) Nanosci. Nanotech. 2:47–53; Lee, J., et al. (2001) J. Nanosci. Nanotech. 1:59–63; Gao, M., et al. (2000) J. Appl. Phys. 87:2297–2302; and Onisuka, O., et al. (1996) J. Appl. Phys. 80:4067. Recently, trilayer hybrid organic molecule-QD LED was demonstrated See Coe, S., et al. (2002) Nature 420:800. Unfortunately, the fabrication of the organic molecule-QD LEDs relies on phase segregation techniques based on differences in size and chemistry of the QDs and organic molecules, and is therefore only applicable for organic molecule-QD LEDs and not PQD-LEDs. Further, the methods for making the organic molecule-QD LED is not viable for sandwiching multilayers of QDs between organic layers, as phase segregation of QDs towards the top of organic molecule layer will not occur if the amount of QDs is more than one or few monolayers. Emission from only one monolayer of QDs may not satisfy the high brightness requirements of commercial applications.
Thus, a need exists for a multilayer PQD-LED and methods for making thereof.